Creating a Client-Server Database System with Windows 95 and Linux

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Here's the way to develop a dial-on-demand database cluster in Linux.

About half a year ago, we began a project called NORA to develop an information system for a private dental clinic in Hong Kong. The basic requirement was that the clinical information, including patient folders, appointment books, laboratory work, etc., could be retrieved and edited by any client PC in the clinic. In addition, the users hoped they could access the data from another clinic using the same system. The system is now in beta testing. We gained some valuable experience during this project, which may be useful for someone wishing to develop a similar system, especially for small- to medium-sized businesses.

We established the following requirements:

  • a client-server database system

  • multi-site (de-centralized)

  • connectivity between LANs on demand

  • dial-up service

  • Windows 95 client

  • Big5 Character set support

  • low transaction rate

  • portability

Since the system would be needed by several users (a dentist and nurses) at the same time, a client-server system is expected. The users do not know much about computers, but they do know Microsoft. They insist on using Windows 95 as the operating system of the client PC, so that they can use their favorite office suite with the same machine. For the server part, they have no preference, so we could decide. We considered both Windows NT and Linux. After considering the stability, ease of installation, cost, flexibility and the requirements listed above, we chose Linux. We think we made the right choice; otherwise, the other system requirements could not be easily fulfilled.

The system is used by a group of several clinics. Users wished to retrieve and update all data easily from any clinic. We considered implementing the system on a single big server, with all clinics connected to it by telephone line or ISDN. However, we found that not only are the communication costs and efficiency worse than the decentralized system (i.e., each clinic has its own server), but also much work would be necessary if another clinic joined the centralized system, since the data in both databases would need to be merged.

As we chose to have one server in each clinic, the connections between clinics should be made on demand, i.e., the connection should be established only when needed. We could install a modem for each client, so that one could dial the server of another clinic to access the data independently. However, this is not an effective method, since every client machine would need a modem and telephone line, and most of the time they are idle. We proposed that the connection be established by the servers, and the clients access the data at another clinic through the servers on demand.

We tried to use diald (dial daemon) on Linux to provide this function. However, most of the documentation on diald assumes the user is using it on a stand-alone workstation or to dial an ISP to access the Internet. The consequence is that the connection is not two-way, i.e., the machine on the Internet cannot access the local workstations. Moreover, the configuration in the document did not consider having dial-in service on the same machine, and the two kinds of service may or may not be compatible.

We found a way to configure diald and dial-in service on Linux harmoniously. Thus, all machines in one clinic can access the database server in another clinic based on dial-on-demand, while the machines in the other clinic can access the database in the first clinic at the same time.

Dial-in service is needed for the dial-in request from the server in another clinic to connect the two LANs. Moreover, the users want to access the data, even when they are at home, by a stand-alone Windows 95 workstation with a modem.

As mentioned above, the users insist on using Windows 95 as their front end. Finding proper method for connecting the client software in Windows 95 to display the data in the Linux server was a problem. This is because some of the database servers for Linux do not provide this feature.

Another constraint for the server is that it must support Big5 characters, since most of the patients use their Chinese name and address for registration. This almost forces us to the final choice of database server, the MySQL server.

We estimated the transaction rate of the system server and found it should be relatively low, about ten SQL executions per minute in the peak period. We think this property is common for small- to medium-sized business applications, so the loading performance of the database server is not crucial.

Finally, we always kept portability in mind. Even though the client software is implemented on Windows 95, we hope to port it to another platform in the future.

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